The Montreal Protocol for the protection of the ozone layer, signed in October 1987, mandated the phase out of the use of chlorofluorocarbons (CFCs). Materials more “friendly” to the ozone layer, such as hydrofluorocarbons (HFCs) eg HFC-134a replaced chlorofluorocarbons. The latter compounds have proven to be green house gases, causing global warming and were regulated by the Kyoto Protocol on Climate Change, signed in 1998. The emerging replacement materials, hydrofluoropropenes, were shown to be environmentally acceptable i.e. has zero ozone depletion potential (ODP) and acceptable low global warming potential (GWP).
Currently used blowing agents for thermoset forms include HFC-134a, HFC-245fa, HFC-365mfc that have relatively high global warming potential, and hydrocarbons such as pentane isomers which are flammable and have low energy efficiency. Therefore, new alternative blowing agents are being sought. Halogenated hydroolefinic materials such as hydrofluoropropenes and/or hydrochlorofluoropropenes have generated interest as replacements for HFCs. The inherent chemical instability of these materials in the lower atmosphere provides the low global warming potential and zero or near zero ozone depletion properties desired.
It is convenient in many applications to provide the components for polyurethane or polyisocyanurate foams in pre-blended formulations. Most typically, the foam formulation is pre-blended into two components. The polyisocyanate and optional isocyanate compatible raw materials comprise the first component, commonly referred to as the “A-” side component. A polyol or mixture of polyols, surfactant, catalyst, blowing agent, and other isocyanate reactive and non-reactive components comprise the second component, commonly referred to as the “B-” side component. Accordingly, polyurethane or polyisocyanurate foams are readily prepared by bringing together the A- and B-side components either by hand mix for small preparations and, preferably, machine mix techniques to form blocks, slabs, laminates, pour-in-place panels and other items, spray applied foams, froths, and the like.
It has been found that the B-side composition of two-component systems have reduced shelf-life, especially those systems which use certain hydrohaloolefins such as HFO-1234ze and HCFO-1233zd. Normally when foam is produced by bringing together the A and B side components, good foam is obtained. However, if the polyol pre-mix composition (B-side) containing hydrohaloolefins is aged prior to treatment with the polyisocyanate (A-side), the foams are of lower quality and may even collapse during the formation of the foam. The poor foam structure is believed to be attributed to the reaction of certain catalysts with certain hydrohaloolefins, including HFO-1234ze and HCFO-1233zd, which results in the partial decomposition of the blowing agent and, subsequently, the undesirable modification of the polymeric silicone surfactants.
One way to overcome this problem, is by separating the blowing agent, surfactant, and catalyst, and introducing them using as separate streams from the “A-” or “B-” side components, a three stream/component methodology. However, a solution that would not require such reformulation or process change would be preferred. A more favorable method may be to utilize a technology to protect active components such as catalysts and surfactants from their reaction with the blowing agent in the B-side during storage, such as encapsulation using a polymer that its crystallization properties can be thermally tailored to the system.
The commonly used catalysts for polyurethane chemistry can be classified into two broad categories: amine and metallic compounds Amine catalysts are generally selected based on whether they drive the gel catalysis (or polymerization) reaction, in which polyfunctional isocyanates react with polyols to form polyurethane, or the blow catalysis (or gas-producing) reaction in which the isocyanate reacts with water to form polyurea and carbon dioxide Amine catalysts can also drive the isocyanate trimerization reaction. Since some amine catalysts will drive all three reactions to some extent, they are often selected based on how much they favor one reaction over another.
U.S. Patent Application Publication No. 2009/0099274 discloses the use of sterically hindered amines that have low reactivity with hydrohaloolefins in foaming systems. Sterically hindered amines are known to be gelling catalysts. Gelling catalysts are typically tertiary amines characterized in that they have higher selectivity for catalyzing the gelling or urethane reaction over the blowing or urea reaction. These catalysts are expected to perform poorly in systems containing high concentrations of water because of their inability to activate water towards isocyanate.
US Patent Application Publication No. 2009/0099273 discloses that . . . “A shortcoming of two-component systems, especially those using certain hydrohaloolefins, including, HFO-1234ze and HFCO-1233zd is the shelf-life of the B-side composition. Normally when foam is produced by bringing together the A and B component, good foam is obtained. However, if the polyol premix composition is aged, prior to treatment with the polyisocyanate, the foam are of lower quality and may even collapse during the formation of foam”, and discloses the use of non-silicone surfactants to stabilize the B-side.
U.S. Pat. No. 6,224,793 discloses the encapsulation of active agents such as catalysts curing agents or accelerators useful in preparing polyurethane to provide for one-part curable compositions which do not require shipment in two parts, an A-side and a B-side. The encapsulated active agents can be designed to release the active agent at a desired temperature. The encapsulated active agents disclosed demonstrate stability for greater than 3 days when exposed to ambient conditions (about 23° C. and about 50 percent relative humidity) and even more preferably for 5 days or greater.
The object of the present invention is to provide novel method of stabilizing polyol blends in presence of low GWP blowing agents by encapsulating of active components such as catalysts and surfactants.